Abstract

Beryl is a common accessory mineral in the hybrid NYF + LCT Julianna pegmatite system, exposed in a quarry at Piława Górna in Lower Silesia, SW Poland. In pods with the LCT-type mineralization it forms zoned, yellowish, white to pinkish, Cs-enriched crystals (up to 16.56 Cs2O wt.%) with compositions at the crystal rims evolving to pezzottaite, i.e., a Cs-dominant mineral of the beryl group, with the empirical formula: (Cs0.755Na0.059Ca0.024K0.008Rb0.0060.148)Σ1(Be1.993Li0.961Si0.046)Σ3(Al1.993Mn0.007)Σ2[Si6O18]. Textural evidence indicates that the Cs-bearing beryl crystallized from a residual melt with high contents of fluxes and pezzottaite from hydrothermal fluids with Cs concentrations increased significantly due to crystallization of cleavelandite that suppressed the activity of Na. The Julianna pegmatitic system at Piława Górna is the third confirmed occurrence of pezzottaite worldwide. The mineral, similarly to pezzottaite in the type occurrence in Madagascar, formed in a pegmatite with a hybrid NYF + LCT signature.

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